Taylor Swift Dedicates 'The Best Day' to Her Mom & Camila Cabello's Mom at Reputation Tour Show

Kevin Mazur/TAS18, Getty Images

Taylor Swift performs on stage during the Reputation World Tour at Levi's Stadium on May 12, 2018 in Santa Clara, Calif.

Cue the tears: Taylor Swift treated the audience at Saturday night's concert to a rare live performance of "The Best Day," in honor of her mother and tour opener Camila Cabello's mother.

Swift sang the sweet, sentimental Fearless track on Mother's Day eve (May 12) in Santa Clara, Calif., during the acoustic portion of her Reputation Stadium Tour set -- apparently by request of Cabello, her tourmate and friend.

"She wants to dedicate this one to her mom," Swift said. The two were on the same page: "I want to dedicate this one to my mom," she added.

"And I want you to think about anybody in your life who has mothered you and been there for you and made you who you are," she told the crowd. "This is called 'The Best Day.'"

With lyrics like "Now I know why the all the trees change in the fall/ I know you were on my side/ Even when I was wrong/ And I love you for giving me your eyes/ Staying back and watching me shine," the song was a touching choice to add to her Reputation Tour set list. (Swift has been swapping in a new acoustic song each night -- "All Too Well," "Wildest Dreams" and "The Best Day" have made appearances so far -- while on one of the B-stages at her show.)

The "Delicate" singer even shared a short video from the performance as a temporary Instagram story on Sunday, writing, "Happy Mother's Day."

Watch clips of Swift introducing and performing "The Best Day" below.

SHE IS SINGING BEST DAY SKGSSKSHSK #repTourSantaClara pic.twitter.com/5D5NU6Iiaz

— kate (@jKAErowling) May 13, 2018